Sediment transport time measured with U-series isotopes; results from ODP North Atlantic drift site 984

Online Access: Get full text
doi: 10.1016/j.epsl.2006.06.004
Author(s): DePaolo, Donald J.; Maher, Kate; Christensen, John N.; McManus, Jerry
Author Affiliation(s): Primary:
University of California, Berkeley, Department of Earth and Planetary Science, Berkeley, CA, United States
Other:
Lawrence Berkeley National Laboratory, United States
Woods Hole Oceanographic Institution, United States
Volume Title: Earth and Planetary Science Letters
Source: Earth and Planetary Science Letters, 248(1-2), p.394-410. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0012-821X CODEN: EPSLA2
Note: In English. 71 refs.; illus., incl. 1 table, sketch map
Summary: High precision uranium isotope measurements of marine clastic sediments are used to measure the transport and storage time of sediment from source to site of deposition. The approach is demonstrated on fine-grained, late Pleistocene deep-sea sediments from Ocean Drilling Program Site 984A on the Bjorn Drift in the North Atlantic. The sediments are siliciclastic with up to 30% carbonate, and dated by δ18O of benthic foraminifera. Nd and Sr isotopes indicate that provenance has oscillated between a proximal source during the last three interglacial periods - volcanic rocks from Iceland - and a distal continental source during glacial periods. An unexpected finding is that the 234U/238U ratios of the silicate portion of the sediment, isolated by leaching with hydrochloric acid, are significantly less than the secular equilibrium value and show large and systematic variations that are correlated with glacial cycles and sediment provenance. The 234U depletions are inferred to be due to α-recoil loss of 234Th, and are used to calculate "comminution ages" of the sediment - the time elapsed between the generation of the small (≤50 µm) sediment grains in the source areas by comminution of bedrock, and the time of deposition on the seafloor. Transport times, the difference between comminution ages and depositional ages, vary from less than 10 ky to about 300 to 400 ky for the Site 984A sediments. Long transport times may reflect prior storage in soils, on continental shelves, or elsewhere on the seafloor. Transport time may also be a measure of bottom current strength. During the most recent interglacial periods the detritus from distal continental sources is diluted with sediment from Iceland that is rapidly transported to the site of deposition. The comminution age approach could be used to date Quaternary non-marine sediments, soils, and atmospheric dust, and may be enhanced by concomitant measurement of 226Ra/230Th, 230Th/234U, and cosmogenic nuclides.
Year of Publication: 2006
Research Program: ODP Ocean Drilling Program
Key Words: 06 Petrology, Sedimentary; 24 Surficial Geology, Quaternary Geology; Absolute age; Actinides; Alkaline earth metals; Atlantic Ocean; Cenozoic; Deposition; Geochronology; Grain size; ICP mass spectra; Isotope ratios; Isotopes; Leaching; Leg 162; Marine sediments; Mass spectra; Metals; Nd-144/Nd-143; Neodymium; North Atlantic; O-18/O-16; ODP Site 984; Ocean Drilling Program; Oxygen; Pleistocene; Precision; Quaternary; Radioactive decay; Radioactive isotopes; Rare earths; Recoil effect; Sediment transport; Sedimentation; Sedimentation rates; Sediments; Spectra; Sr-87/Sr-86; Stable isotopes; Strontium; Thermal ionization mass spectra; U-238/U-234; Upper Pleistocene; Uranium; Uranium disequilibrium
Coordinates: N612532 N612532 W0240457 W0240457
Record ID: 2008016331
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands